If I have two boards, both with a directional antenna, can I determine the location of one of them from the other, or will I need three or more boards in order to triangulate the position of one of them?

You could do distance and if you knew the bearing then from that position but based on physics/ geometry you need at least one more to do 2D position. I was actually considering doing something similar to aircraft ILS system for UAVs

what did you end up doing? a fleet of drones that could pinpoint each other in 3d would be great! shouldn't be too hard either, in theory, but i don't know if the software for triangulation is there for flutter yet.

For a project I am working on, we are currently doing this with Zigbee while waiting for Flutter and it's improved range.

We use a 12-14db gain Yagi. We rotate the antenna and map the signal strength to indicate where the base signal is located. As @jet_flyer indicated you will need a second reading to triangulate for distance.

I have talked to @taylor about using the Flutter for Time-Of-Flight calculations for distance but he said the the clock used on Flutter is not accurate enough for TOF. It has too much drift. This is not a knock on Flutter as TOF has very, very tight timing requirements. Once Flutter is fully released I'll see about a possible replacement part for Flutter to tighten the timing.

If you have a directional antenna and you can rotate it, then yes you can determine the angle between two devices with a rough estimate of distance based on RSSI.

As far as time of flight, you need a clock that operates in the GHz range, and Flutter only uses a 40MHz clock. You also need custom analog electronics on the RF front end to do some tricky stuff with the radio wave as it hits the antenna. It's basically very complex to do TOF measurements on a platform like this. If you operate in the 5.8GHz range or above it's not too bad, and some chips are now being made available that support this. But 915MHz is very low frequency for TOF measurement, so Flutter's radio system simply isn't well cut out for this. I am interested in a module that attaches to Flutter and adds TOF capability but it would be a completely separate radio system operating in a higher frequency band. Positioning is important to Flutter's future goals, but I still haven't pinned down how we will do it.

Rotating an antenna should work pretty well though for angle. You should also be able to rotate a baffle around a Flutter board, but I haven't tested this.

So even if Flutter is not "well suited" for TOF calculations, does it still have the capability of performing them? I think that if it had an accuracy of even 5-10 meters it would still be useful for many applications.

Like 'My drone landed somewhere in this field........ but where.'Narrowing down to even 20'x20' would be awesome. I suppose there are other possibly better ways of doing this specific example though.....